length = float(input('a:'))#输入a
breadth = float(input('b:'))#输入b
print('a+b =', length + breadth)
print('a-b =', length - breadth)
print('a*b =', length * breadth)
print('a/b =', length / breadth)

radii = float(input('输入圆的半径:'))#输入半径
import math
print('圆的周长：', 2 * radii * math.pi)#2πr
print('圆的面积：' , math.pi * radii ** 2)#πr^2